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[ScalarEvolution] refactor: extract interface getGEPExpr

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Summary:
This allows other passes (such as SLSR) to compute the SCEV expression for an
imaginary GEP.

Test Plan: no regression

Reviewers: atrick, sanjoy

Reviewed By: sanjoy

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9786

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237589 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jingyue Wu 2015-05-18 17:03:25 +00:00
parent febe7813c8
commit 2703007b7b
3 changed files with 82 additions and 56 deletions
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9
include/llvm/Analysis/ScalarEvolution.h
View File

@ -657,6 +657,15 @@ namespace llvm {
SmallVector<const SCEV *, 4> NewOp(Operands.begin(), Operands.end());
return getAddRecExpr(NewOp, L, Flags);
}
/// \brief Returns an expression for a GEP
///
/// \p PointeeType The type used as the basis for the pointer arithmetics
/// \p BaseExpr The expression for the pointer operand.
/// \p IndexExprs The expressions for the indices.
/// \p InBounds Whether the GEP is in bounds.
const SCEV *getGEPExpr(Type *PointeeType, const SCEV *BaseExpr,
const SmallVectorImpl<const SCEV *> &IndexExprs,
bool InBounds = false);
const SCEV *getSMaxExpr(const SCEV *LHS, const SCEV *RHS);
const SCEV *getSMaxExpr(SmallVectorImpl<const SCEV *> &Operands);
const SCEV *getUMaxExpr(const SCEV *LHS, const SCEV *RHS);

96
lib/Analysis/ScalarEvolution.cpp
View File

@ -2926,6 +2926,56 @@ ScalarEvolution::getAddRecExpr(SmallVectorImpl<const SCEV *> &Operands,
return S;
}
const SCEV *
ScalarEvolution::getGEPExpr(Type *PointeeType, const SCEV *BaseExpr,
const SmallVectorImpl<const SCEV *> &IndexExprs,
bool InBounds) {
// getSCEV(Base)->getType() has the same address space as Base->getType()
// because SCEV::getType() preserves the address space.
Type *IntPtrTy = getEffectiveSCEVType(BaseExpr->getType());
// FIXME(PR23527): Don't blindly transfer the inbounds flag from the GEP
// instruction to its SCEV, because the Instruction may be guarded by control
// flow and the no-overflow bits may not be valid for the expression in any
// context.
SCEV::NoWrapFlags Wrap = InBounds ? SCEV::FlagNSW : SCEV::FlagAnyWrap;
const SCEV *TotalOffset = getConstant(IntPtrTy, 0);
// The address space is unimportant. The first thing we do on CurTy is getting
// its element type.
Type *CurTy = PointerType::getUnqual(PointeeType);
for (const SCEV *IndexExpr : IndexExprs) {
// Compute the (potentially symbolic) offset in bytes for this index.
if (StructType *STy = dyn_cast<StructType>(CurTy)) {
// For a struct, add the member offset.
ConstantInt *Index = cast<SCEVConstant>(IndexExpr)->getValue();
unsigned FieldNo = Index->getZExtValue();
const SCEV *FieldOffset = getOffsetOfExpr(IntPtrTy, STy, FieldNo);
// Add the field offset to the running total offset.
TotalOffset = getAddExpr(TotalOffset, FieldOffset);
// Update CurTy to the type of the field at Index.
CurTy = STy->getTypeAtIndex(Index);
} else {
// Update CurTy to its element type.
CurTy = cast<SequentialType>(CurTy)->getElementType();
// For an array, add the element offset, explicitly scaled.
const SCEV *ElementSize = getSizeOfExpr(IntPtrTy, CurTy);
// Getelementptr indices are signed.
IndexExpr = getTruncateOrSignExtend(IndexExpr, IntPtrTy);
// Multiply the index by the element size to compute the element offset.
const SCEV *LocalOffset = getMulExpr(IndexExpr, ElementSize, Wrap);
// Add the element offset to the running total offset.
TotalOffset = getAddExpr(TotalOffset, LocalOffset);
}
}
// Add the total offset from all the GEP indices to the base.
return getAddExpr(BaseExpr, TotalOffset, Wrap);
}
const SCEV *ScalarEvolution::getSMaxExpr(const SCEV *LHS,
const SCEV *RHS) {
SmallVector<const SCEV *, 2> Ops;
@ -3700,52 +3750,16 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
/// operations. This allows them to be analyzed by regular SCEV code.
///
const SCEV *ScalarEvolution::createNodeForGEP(GEPOperator *GEP) {
Type *IntPtrTy = getEffectiveSCEVType(GEP->getType());
Value *Base = GEP->getOperand(0);
// Don't attempt to analyze GEPs over unsized objects.
if (!Base->getType()->getPointerElementType()->isSized())
return getUnknown(GEP);
// Don't blindly transfer the inbounds flag from the GEP instruction to the
// Add expression, because the Instruction may be guarded by control flow
// and the no-overflow bits may not be valid for the expression in any
// context.
SCEV::NoWrapFlags Wrap = GEP->isInBounds() ? SCEV::FlagNSW : SCEV::FlagAnyWrap;
const SCEV *TotalOffset = getConstant(IntPtrTy, 0);
gep_type_iterator GTI = gep_type_begin(GEP);
for (GetElementPtrInst::op_iterator I = std::next(GEP->op_begin()),
E = GEP->op_end();
I != E; ++I) {
Value *Index = *I;
// Compute the (potentially symbolic) offset in bytes for this index.
if (StructType *STy = dyn_cast<StructType>(*GTI++)) {
// For a struct, add the member offset.
unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
const SCEV *FieldOffset = getOffsetOfExpr(IntPtrTy, STy, FieldNo);
// Add the field offset to the running total offset.
TotalOffset = getAddExpr(TotalOffset, FieldOffset);
} else {
// For an array, add the element offset, explicitly scaled.
const SCEV *ElementSize = getSizeOfExpr(IntPtrTy, *GTI);
const SCEV *IndexS = getSCEV(Index);
// Getelementptr indices are signed.
IndexS = getTruncateOrSignExtend(IndexS, IntPtrTy);
// Multiply the index by the element size to compute the element offset.
const SCEV *LocalOffset = getMulExpr(IndexS, ElementSize, Wrap);
// Add the element offset to the running total offset.
TotalOffset = getAddExpr(TotalOffset, LocalOffset);
}
}
// Get the SCEV for the GEP base.
const SCEV *BaseS = getSCEV(Base);
// Add the total offset from all the GEP indices to the base.
return getAddExpr(BaseS, TotalOffset, Wrap);
SmallVector<const SCEV *, 4> IndexExprs;
for (auto Index = GEP->idx_begin(); Index != GEP->idx_end(); ++Index)
IndexExprs.push_back(getSCEV(*Index));
return getGEPExpr(GEP->getSourceElementType(), getSCEV(Base), IndexExprs,
GEP->isInBounds());
}
/// GetMinTrailingZeros - Determine the minimum number of zero bits that S is

33
lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
View File

@ -509,31 +509,34 @@ void StraightLineStrengthReduce::allocateCandidatesAndFindBasisForGEP(
if (GEP->getType()->isVectorTy())
return;
const SCEV *GEPExpr = SE->getSCEV(GEP);
Type *IntPtrTy = DL->getIntPtrType(GEP->getType());
SmallVector<const SCEV *, 4> IndexExprs;
for (auto I = GEP->idx_begin(); I != GEP->idx_end(); ++I)
IndexExprs.push_back(SE->getSCEV(*I));
gep_type_iterator GTI = gep_type_begin(GEP);
for (auto I = GEP->idx_begin(); I != GEP->idx_end(); ++I) {
for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I) {
if (!isa<SequentialType>(*GTI++))
continue;
Value *ArrayIdx = *I;
// Compute the byte offset of this index.
const SCEV *OrigIndexExpr = IndexExprs[I - 1];
IndexExprs[I - 1] = SE->getConstant(OrigIndexExpr->getType(), 0);
// The base of this candidate is GEP's base plus the offsets of all
// indices except this current one.
const SCEV *BaseExpr = SE->getGEPExpr(GEP->getSourceElementType(),
SE->getSCEV(GEP->getPointerOperand()),
IndexExprs, GEP->isInBounds());
Value *ArrayIdx = GEP->getOperand(I);
uint64_t ElementSize = DL->getTypeAllocSize(*GTI);
const SCEV *ElementSizeExpr = SE->getSizeOfExpr(IntPtrTy, *GTI);
const SCEV *ArrayIdxExpr = SE->getSCEV(ArrayIdx);
ArrayIdxExpr = SE->getTruncateOrSignExtend(ArrayIdxExpr, IntPtrTy);
const SCEV *LocalOffset =
SE->getMulExpr(ArrayIdxExpr, ElementSizeExpr, SCEV::FlagNSW);
// The base of this candidate equals GEPExpr less the byte offset of this
// index.
const SCEV *Base = SE->getMinusSCEV(GEPExpr, LocalOffset);
factorArrayIndex(ArrayIdx, Base, ElementSize, GEP);
factorArrayIndex(ArrayIdx, BaseExpr, ElementSize, GEP);
// When ArrayIdx is the sext of a value, we try to factor that value as
// well. Handling this case is important because array indices are
// typically sign-extended to the pointer size.
Value *TruncatedArrayIdx = nullptr;
if (match(ArrayIdx, m_SExt(m_Value(TruncatedArrayIdx))))
factorArrayIndex(TruncatedArrayIdx, Base, ElementSize, GEP);
factorArrayIndex(TruncatedArrayIdx, BaseExpr, ElementSize, GEP);
IndexExprs[I - 1] = OrigIndexExpr;
}
}